Circuit for the contactless control of thyristors

ABSTRACT

Circuit for contactless control of thyristor is response to approachment of predetermined electromagnetic field influencing means; input means are provided for supplying input pulses to said circuit and control means are coupled to thyristor for operating same in response to input pulse in predetermined amplitude range; translating means are coupled to the input means and control means for applying the input pulses to control means, the translating means includes circuit electromagnetic means operable in response to approachment of said influencing means to establish said input pulse in said predetermined amplitude range.

United States Patent Dosch et al.

[54] CIRCUIT FOR THIB CONTACTLESS CONTROL OF THYRISTORS [72] Inventors:Peter Dosch, Rankstrasse l5; Emil Benz, Iarchenstrasse 10, both ofCanton of St. Gall, Switzerland 22 Filed:. Sept. 18,1968

211 Appl.No.: 760,528

[30] Foreign Application Priority Data Sept. 27, 1967 Switzerland ..13136/67 [52] US. Cl. ..307/252 N, 307/287, 307/288, 307/324, 317/D1G.'2,328/5, 331/65 [51] Int. Cl. ..H0lh 36/00, H031; 17/70, I-I03k 17/72 [58]Field of Search ..307/247, 262, 287, 288, 305, 307/324; 317/123 P, 146,123, DIG. 2; 328/5;

[56] References Cited UNITED STATES PATENTS 2,985,848 5/1961 Raffaelli..317/146 3,147,408 9/1964 Yamamoto et al.. 317/123 3,161,759 12/1964Gambill et a1. 307/287 3,195,043 7/1965 Burig et a1. 340/258 Feb. 22,1972 Galloway J. I-I., Using the Triac for Control of AC Power, 3/66 pp.5- 19. G. E. Transistor Manual; p. 312- 316, 320- 333, Copyright 1964.

Primary ExaminerDonald D. Forrer Assistant Examiner-L. N. AnagnosAttorneyWard, McElhannon, Brooks & Fitzpatrick 57] ABSTRACT Circuit forcontactless control of thyristor is response to approachment ofpredetermined electromagnetic field influencing means; input means areprovided for supplying input pul- 3,197,658 7/ 1965 Byrnes et al..317/12 ses to said circuit and control means are coupled to thyristor3'200305 8/1965 Atkms, 317/123 for operating same in response to inputpulse in predeter- 3201'679 8/1965 Buchanan" "307/287 mined amplituderange; translating means are coupled to the 3,201,774 8/1965 Uemura..317/ 123 input means and control means applying the input pulses3,206,696 9/1965 Wright." 331/ 1 1 to control means, the translatingmeans includes circuit elec- 3,215,950 11/1965 Re nerm. 331/11tromagnetic means operable in response to approachment of 3,223,35212/1965 wright 307/287 said influencing means to establish said inputpulse in said 3,254,313 5/1966 Atkins et al ..317/123 predeterminedamplitude 3,255,380 6/1966 Atkins et a1 ..317/123 3,265,991 8/1966Ferguson ..331/ l 1 1 13 Claims, 9 Drawing Figures PATENTEDFEBZZ I972 3,44,754

SHEET 3 BF 3 l N VENTURS Para/e LbscH BY 671/4 560 CIRCUIT FOR THECONTACTLESS CONTROL OF THYRISTORS This invention relates to switchingcircuits and, more parcontrol of thyristors.

Most known proximity switching circuits, sometimes referred to ascontactless initiators, operate in accordance with the principle whereina magnetic or like field set up by the switching circuit, is influencedby the approachment of a metallic object to change the impedance of theswitching circuit, and thus change the voltage/current relationship ofthe circuit to indicate the presence of the object. Thus for example, inone known arrangement a coil is arranged in a balanced bridge circuitwhich is energized with a high frequency source; and, upon theapproachment of the metallic object, the bridge is unbalanced by thedisturbance of the magnetic field set up by the coil. In anotherarrangement, the coil is incorporated as a part of an oscillator circuitand the approachment of the metallic object within the vicinity of themagnetic field set up by the coil distunes or dampens the oscillatorthereby changing the amplitude of the output signal of the oscillator.In both of these described arrangements, a signal indicating theproximity of the metal object to the circuit is produced from the outputsignals of these described switching arrangements in a suitable outputcircuit.

Proximity switching circuits are used, by way of example, to provide anindication of the relative position of a metallic object or the likewithout using any contacts; and very often are made part of a verysimple regulating circuit wherein the proximity switching circuitsenses, for example, the turning of a measuring instrument, or theposition of an element indicating the actual value of a regulating path(e.g., a membrane) to provide a control signal. Usually, this control oroutput signal is then used to control a relay which in turn controls aregulating circuit or the like. As those skilled in the art appreciate,the use of a relay, and thus contacts, at the output of a proximityswitching circuit is, however, subject to many drawbacks. In order toavoid the use of contacts at this point the relay could be replaced witha contactless switching circuit controlled or switched by the outputsignal of the proximity switching circuit. Typical contactless switchingcircuits may include a thyristor switching element, two thyristors inantiparallel relationship, a thyristor controlled bridge, a triac or thelike.

The substitution of a contactless switching circuit for a relay at theoutput of the proximity circuit, however, has the disadvantage that thecoil in the proximity switch must be energized with a high-frequencysource to provide a first control signal, and then a direct voltagesignal must be produced from this control signal. Thereafter, thisdirect voltagesignal must again be converted into a high-frequencysignal for providing the ignition pulse for the contactless switchingcircuit. Obviously this method of eliminating contacts is verycomplicated and costly.

The present invention provides a very simple and inexpensive means foreliminating contacts at the output of a proximity switching circuit andavoids many of the drawbacks of the solution discussed above.

In accordance with one aspect of the present invention, there isprovided a switching circuit for controlling a thyristor operatedcircuit in response to the approachment in the vicinity of switchingcircuit of a predetermined electromagnetic field influencing means, suchas a metallic object or the like. The switching circuit constructed inaccordance with the present invention comprises input means forsupplying at least one electrical input pulse, and preferably a trainthereof, to said switching circuit and control means coupled to the gateelectrode of the thyristor for controlling the operation thereof inresponse to an applied pulse in a predetermined amplitude range.Translating means are coupled to said input means and said control meansfor applying said input pulse to said control means. The translatingmeans includes circuit electromagnetic means, such as an induction coilor the like, operable in response to the approachment of the saidinfluencing means, to establish said input pulse in said predeterminedamplitude range.

In accordance with another aspect of the present invention, thethyristor operated circuit includes a thyristor having a gate electrodeand two other electrodes having conduction therebetween when saidthyristor is in the on-state, and an output load and alternating powersupply input means connected between said two other electrodes. Theinput means of the switching circuit and the alternating power supplyinput means of said thyristor operated circuit are synchronized, andpreferably energized from a common alternating power source. Thus, theinputmeans of the switching circuit may include an RC charging circuitenergized by said alternating power supply input means of said thyristoroperated circuit and a trigger circuit connected to said chargingcircuit and said translating means to provide the necessary inputpulses. In addition, the control means may also comprise a suitabletrigger circuit operable in response to said pulses in saidpredetermined amplitude to control saidthyristor. The trigger circuitsutilized in both the input means and the control means may includevoltage breakdown triggering elements, transistor switching circuits orthe like.

In accordance with another aspect of the present invention, the controlmeans maintains the thyristor in substantially nonconductive state whenits applied signal is within said predetermined amplitude range andplaces said thyristor in the conductive state when the applied signal iswithin a second amplitude range. Of course, in this arrangement, theinput pulse supplied by said input means is within said second amplituderange such that the thyristor is placed in the conductive state when theelectromagnetic field influencing means is not in said vicinity and ismaintained in the nonconductive state when said influencing means iswithin said vicinity.

There has thus been outlined rather broadly the more important featuresof the invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described hereinafterand which will form the subject of the claims appended hereto. Thoseskilled in the art will appreciate that the conception upon which thisdisclosure is based may readily be utilized as a basis for the designingof other structures for carrying out the several aspects of theinvention. It is important therefore, that the claims be regarded asincluding such equivalent constructions as do not depart from the spiritand scope of the invention.

Certain specific applications of the invention have been chosen forpurposes of illustration, and are shown in the accompanying drawingforming a part of the specification wherein:

FIG. 1 shows in schematic form a circuit constructed in accordance withthe present invention for controlling a thyristor and utilizing voltagebreakdown triggering elements;

FIG. 2 shows in schematic form another circuit, similar to that shown inFIG. 1, for regulating the output load of the thyristor;

FIG. 3 shows a modified form of the circuit shown in FIG. I which isespecially suitable for utilizing triggering elements having similartriggering voltages;

FIG. 4 shows a modified form of the circuit shown in FIG. 3 andutilizing unijunction transistors;

FIG. 5 shows wave forms schematically illustrating the temporary courseof the ignition voltage and of the ignition voltage threshold of theunijunction transistor utilized in FIG. 4',

FIG. 6 shows a modified form of the circuit shown in FIG. 1, usingtransistor switching circuits instead of trigger elements;

FIG. 7 shows in schematic form another circuit constructed in accordancewith the present invention;

FIG. 8 shows still another schematic version of a circuit constructed inaccordance with the present invention; and

FIG. 9 shows a modified form of the circuit shown in FIG. 1 and adaptedfor utilizing coupled transformers as the electromagnetic influencedelement.

thyristor controlled output circuit, shown generally at 14, in-

cluding a thyristor l6 and an'output load 18 coupledin series across thealternating power source 20. The thyristor 16 comprises a gate electrode22and two other electrodes 24 and 26 having conduction therebetween whenthe thyristor is in the on-state, and which are connected to the outputload 18 and to one terminal of the alternating power source 20. Inaddition, the circuit includes input means, shown generally at 28, forsupplying electrical input pulses through the circuit. The input means28 includes an RC charging circuit comprising resistor 30 and capacitor32 connected in series across the alternating power source 20, and atrigger circuit 34 comprising a voltage breakdown triggering element,such as the diac 36 and a resistor 38 shown in FIG. 1. Translatingcircuit means, shown generally at 40, is connected between the resistor38 and one side of the alternating power source'20, and functions totranslate the input pulses supplied by the input circuit 28 to a controlcircuit 42 coupled to the thyristor 16. As shown in FIG. 1, thetranslating circuit means 40 includes circuit electromagnetic means,such as the coil 44, the magnetic field of which is influenced by theapproachment of the vane 12. The control circuit 42 comprises a voltagebreakdown trigger element, such as the diac 46 shown in FIG. 1, which isconnected between the translating circuit means 40 and the gateelectrode 22 of the thyristor 16.

In operation, the voltage supplied by the alternating power supply 20charges the capacitor 32 via the resistor 30 until the voltage breakdownvalue of the diac 36 is reached, thus igniting the same. Upon ignitionof the diac 36, pulse current flows through same, the resistor 38, andthe coil 44 to produce a pulse of the shape shown in FIG. 1 which isapplied to the control circuit 42. It will be appreciated that bysuitably choosing the RC time constant t" of the capacitor 32 and theresistor 30, the exact moment at which this pulse is applied to thecontrol circuit 42 and thus diac 46 may be fixed. Preferably, when thevane 12 is not within the vicinity of circuit 10, the pulse applied tothe control circuit 42 will be so intense or within a predeterminedamplitude range, that it will ignite the diac 46. The ignition of thediac 46 will, of course, in turn ignite the thyristor 16 toconnect theoutput load 18 across the alternating power source 20. When the vane 12is within the vicinity of the circuit 10, however, the vaneinfluences'the magnetic field of the coil 44, and thus its voltagecurrent relationship, to dampen the amplitude of the input pulsespassing through the translating means 40 to a second amplitude rangewhich does not trigger diac 46. Thus, as the vane 12 moves closer andcloser to the circuit 10, and thus to the coil 44, the coil is dampenedand the pulse produced thereacross to the control circuit 42 graduallybecomes smaller and smaller until it is below the ignition voltage ofthe diac 46. At this position, and upon any subsequent furtherapproachment of the vane 12 to the circuit 10, the thyristor 16 is notignited, and thus the output load 18 is switched off from thealternating input power supply 20. Stated another way, the thyristor 16is placed in the onstate when the object is not within the vicinity ofthe circuit,

and is maintained in the off-state when the metallic vane is within itsvicinity.

. The output load 18 does not have to be connected to the full supplyvoltage of the input power supply 20 and may be controlled in a mannershown schematically in FIG. 2. The circuit 48 shown in FIG. 2 isconstructed and operates substantially the same as that described inconnection with FIG. 1 except for the use 'of an additional RC chargingcircuit, shown generally at 50, and an additional voltage breakdowntriggering circuit, such as the diac 52 shown therein. The RC chargingcircuit comprises a resistor 54 and a capacitor 56 connected in seriesacross the input power supply 20. The diac 52 is connected at one end tothe juncture of resistor 54 and capacitor 56 and to the gate electrode22 of the thyristor 16. The time constant of the RC charging circuit 50is made larger than that of the RC charging circuit defined by theresistor 30 and the capacitor 32 described in connection with FIG. 1.Thus, in operation, and simultaneously with the operation of the circuitas otherwise described above, the capacitor 56 of the charging circuit50 is charged via the resistor 54 until the ignition voltage of the diac52 is reached. At this voltage, the diac 52 is ignited and thus also thethyristor 16. When the vane 12 is not within the vicinity of thecircuit, and since the time constant of the charging circuit 50 islonger than that of RC charging circuit of the input means 28, thethyristor 16 is ignited by the input pulse supplied by the coil 44through the control circuit 42. If, however, the vane 12 is in thevicinity of the circuit, the ignition of the diac 46 of the controlcircuit 42 will not take place, but the thyristor 16 will still beignited upon the delayed ignition of the diac 52. Thus, it will beappreciated by regulating the charging time of the two noted chargingcircuits, the phase cutout of the basic and full load may be selected toselectively determine the power load at output circuit 18. Thisdescribed ignition circuit may be provided in all of remaining circuitsdescribed hereinafter.

It will be appreciated from the above discussion in connection withFIGS. 1 and 2 that the amplitude of the pulse translated by coil 44 willbe smaller than the breakdown voltage of the diac 36 and thus a suitablediac having a voltage breakdown value smaller than that of diac 36 mustbe utilized as diac 46. The circuit 60, shown generally in FIG. 3, is amodified form of the circuit shown in FIG. 1 wherein the breakdownvoltage of the diacs 36 and 46 are substantially the same. The circuit60 is arranged substantially similar to that shown in FIG. 1, exceptthat the coil 44 is coupled to diac 46 via a charging capacitor 62. Inaddition, a voltage divider comprising resistances 64 and 66 isconnected across the charging capacitor 32, and a diode 68 is connectedbetween the voltage divider and diac 46 in the manner shown in FIG. 3.The values of resistances 64, 66 and capacitor 62 are chosen such asthat during the charging of the RC charging circuit of the input means28, the capacitor 62 is charged to a value which when added to theamplitude of the pulse produced'across the coil 44 during the ignitionof the diac 36, produces a value sufficient to trigger the diac 46.Thus, during normal operation of the circuit 60, the RC charging circuitof the input means 28 proceeds to charge to a value sufficient to ignitethe diac 36, and the capacitor 62 similarly charges through theresistances 64,66 and the diode 68 to its mentioned value. When thevoltage across the capacitor 32 has reached that value sufficient toignite the diac 36, the latter is ignited and a pulse is coupled throughthe capacitor 62 and supplemented with the charging voltage thereon toignite the diac 46. Upon the ignition of the diac 36, the diode 68 isback-biased to prevent the capacitor 62 from being quickly discharged.Thus, when the vane 12 is not within the vicinity of the circuit 60, thepulse translated through the capacitor 62 is of a sufficient amplitudeto trigger the diac 46, but when the vane 12 is within the vicinity ofthe circuit, the pulse produced via the coil 44 is reduced in amplitudesufficient that the resultant pulse coupled via the capacitor 62 is nolonger of an amplitude sufficient to trigger the diac 46.

While the circuits described in connection with FIGS. 1, 2 and 3 utilizediacs as trigger elements, obviously other known voltage breakdowntriggering elements may be utilized such as for example trigger diodes,four layer diodes, glowlamps and unijunction transistors. For example,FIG. 4 shows in schematic form a circuit 70 which utilizes unijunctiontransistors 72 and 74 in lieu of diacs 36 and 46 described in connectionwith FIGS. l-3. As shown therein, a Zener diode 76 is connected througha resistance 78 and charging resistor 30 to the power supply 20 andduring the positive excursion of the power input voltage builds avoltage thereacross. The capacitor 32 proceeds to charge to this lattervoltage through resistance 79 until the ignition voltage of theunijunction transistor 72 is reached. At this voltage the unijunctiontransistor 72 is ignited and a pulse is coupled through the resistance38 across the coil 44 to the unijunction transistor 74. Simultaneously,as in the embodiment described in connection with FIG. 3, the condenser62 is charged via the voltage divider consisting of resistors 64 and 66to a voltage which is lower than the ignition voltage of the unijunctiontransistor 74. In normal operation when the vane 12 is not in thevicinity of the circuit 70, the voltage buildup on the condenser 62 andthe amplitude of the pulses transmitted therethrough from the coil 44are sufficient to reach the ignition voltage of the unijunctiontransistor 74, and thus also sufficient to trigger the thyristor 16 andconnect output load 18 to the alternating power supply 20. In thisregard, a resistance 80 may be provided between one of the emitters ofthe unijunction transistors 74 and one side of the power supply 20 toprevent current surges from damaging the respective elements. Upon theapproachment of the vane 12, (not shown) the electromagnetic field ofthe coil 44 is changed so that the sum of the condenser voltage 62 andthe amplitude of the transmitted pulses is not sufficient to ignite theunijunction transistor 74.

' The schematic representation of the operation of the circuit shown inFIG. 4 may be best understood by reference to FIG. 5. There is showntherein in schematic form, the wave forms of the ignition voltage andthe ignition voltage threshold for the unijunction transistor 74 of thecircuit in FIG. 4. The ignition threshold voltage of the unijunctiontransistor 74 is represented by curve 82. As shown in FIG. 5, thevoltage rapidly rises from zero until such time as the Zener diode 76becomes conductive, thereafter the voltage remains substantiallyconstant and follows perhaps a slightly bent curve created by thedynamic inner resistance of the Zener diode 76 and the additionalresistance 78 connected in series with the Zener diode 76. Toward theend of the half cycle of the alternating power supply input, theignition threshold voltage is rapidly reduced to zero and then repeatsitself as described above. The voltage buildup on condenser 62 duringthe operation of the circuit 70 is represented in FIG. 5 by the curve84. As shown therein, the curve 84 indicates that the voltage acrosscondenser 62 follows the ignition threshold voltage shown in curve 82,but at a certain predetermined lag caused by the time constant which isproduced by the resistances of the voltage divider comprisingresistances 64 and 66 and the condenser 62, This time lag causes thedifferences between the ignition threshold voltage 82 and the condenservoltage 84 to become smaller and smaller in the course of the half cycleof the alternating input power source 20.

As discussed above, the voltage 84 of the capacitor 62 is superimposedwith the input pulse voltage of the coil 44, represented in FIG. 5 bythe needlelike pulses 86. It will be appreciated that the voltagedivider resistances 64 and 66 are preferably adjusted so that the firstimpulse provided by the coil 44 adds to the condenser voltage 84 toexceed the ignition threshold voltage 82, and thus ignite the thyristor16 in the manner discussed above. Upon the approachment of the vane 12near the circuit 70, the pulses translated by the coil 44 becomes smallsuch that the initial pulse of the resultant ignition voltage acrosscondenser 62 is insufficient to ignite the unijunction transistor 74. Inthis instance, the first ignition of the unijunction transistor 72 isfollowed by a recharging of the condenser 62 through the resistance 78,and after the lapse of time, a second pulse is provided across the coil44 by the reignition of the unijunction transistor 72 during thesubsequent cycle of the input power source 20. The resultant voltagelevel .across the capacitor 62 may now bring about the ignition of theunijunction transistor 74 and, therefore also of the thyristor 16. Ifthe vane 12 is brought closer to the coil 44, then perhaps only thethird, fourth, fifth, sixth, etc., pulse produced by the unijunctiontransistor 72 may bring about ignition of the unijunction transistor 74.Therefore, the thyristor 18 is ignited later and later, and thus thearrangement may be used as a discontinuously working proportionalregulator whose proportional range is selected by appropriate choice ofresistance 80 and the time constant resulting from the condenser 62 andof the resistors 64 and 66.

The circuit 90 schematically shown in FIG. 6 utilizes transistorswitching circuitry in lieu of diacs 36 and 46 as in FIGS. 1-3. Thus,transistors 92 and 94 are circuit arranged such that each are in offstate during the time that the capacitor 32 is charged in a mannerdescribed heretofore. Thus, by including resistances 96 and 98 in serieswith a Zener diode 100 and connected to transistors 92 and 94 as shownin FIG. 6, as long as the voltage buildup across capacitor 32 is belowthe zener voltage of the Zener diode 100, no conduction is made betweenthis series connection therethrough and thus the transistors 92 and 94are maintained in off state. As soon as the voltage across capacitor 32exceeds the Zener voltage of the Zener diode 100, however, the Zenerdiode 100 becomes conductive and a voltage drop appears across theresistances 96 and 98 which bring transistors 92 and 94 into theconductive range. As soon as one of the transistors 92 and 94 becomesconductive, its base to collector impedance effectively short circuitsZener diode 100 to thereby further increase the voltages drop across theresistances 96 and 98, and thus further turn on the transistors 92 and94. Accordingly, a very quick change in state of transistors 92 and 94is obtained. Consequently, a very rapidly increasing current pulse isfed through the resistor 38 to produce a triggering pulse in the coil44. During this time, the capacitor 62 is charged via the diode 68 toapproximately the Zener voltage of the Zener diode 100. Transistors 102and 104 are also additionally arranged within the circuit such that theyare also in off state during the latter described charging time. Thus,the voltage divider comprising resistances 106 and 108 are selected suchthat the emitter of the transistor 102 is maintained at a very highpotential with respect to its base and thus reversed biased. Since thereis no voltage across the resistance 110 by reason of the reverse bias ofthe transistor 102, transistor 104 is also in off state. If, however,the amplitude of the pulse appearing across coil 44 is higher than thevoltage supplied by the voltage divider 106, 108 to the emitter oftransistor 102, the transistor 102 is made conductive throughthe'resistance 111. This, of course, produces a voltage drop acrossresistance 110 which also brings the transistor 104 into conduction sothat an ignition pulse is fed therethrough to the thyristor 16 via theresistance 112 to ignite the same. A diode 114 may be provided betweenthe collector and base of the transistors 104 and 102 respectively toprevent the thyristor 16 from being directly ignited by the pulse of thecoil 44.

Based on the above disclosure, it will be apparent that othermodifications may be made to produce other significant electricalfunctions. Thus, as shown in FIG, 7, the electric circuit shown in FIG.1 as well as the other electric circuits described hereinabove, may beoperated during both halves of the input alternating power supply 20 bythe use of a diode bridge 116. It will be appreciated, as shown by thewave form of FIG. 7, that the output load 18 is fed by a double wavedirect voltage 118. In another circuit, an alternating voltage outputload may be inserted as shown in FIG. 7 to provide an alternating loadoutput. Also, as shown in FIG. 8 the circuit of FIG. 1 as well as allthe other circuits heretofore described, may utilize a pulse transformer122 connected as shown in FIG. 8 to indirectly control thyristors orother triac configurations. Lastly, as shown in FIG. 9, a transformer124 may be used in lieu of the coil 44 described above. It will be notedthat in this case, no series resistance 38 is necessary.

Thus, it will be seen from the above that the present invention providesa simple and very inexpensive proximity switching circuit which does nothave contacts at its output.

Having thus described the invention with particular reference to thepreferred forms thereof, it will be obvious to those skilled in the artto which the invention pertains, after understanding the invention, thatvarious changes and modifications may be made therein without departingfrom the spirit and scope of the invention as defined by the claimsappended hereto.

What is claimed as new and desired to be secured by Letters Patent is: i

1. A circuit for the touchless control of a thyristor in response to theapproachment in the vicinity of said circuit of a predeterminedelectromagnetic field influencing means, said circuit comprising athyristor controlled output circuit including a thyristor having a gateelectrode and two other electrodes having conduction therebetween whensaid thyristor is in the conductive state, alternating power sourceinputmeans connected across said two other electrodes, pulse circuit meansconnected to and synchronized by said alternating power source inputmeans for providing a triggering pulse at a predetermined time 'afterthe beginning of each alternation of said alternating power source,control means coupled to said gate electrode of said thyristor forcontrolling the operation thereof in response to anapplied pulse in apredetermined amplitude range, and translating means coupled to saidpulse circuit means for applying said triggering pulse to said controlmeans, said translating means including touchless electromagneticcircuit means operable in response to the approachment of saidinfluencing means to establish said input pulse in said predeterminedamplitude range. I

2. A circuit as in claim 1 wherein said control means maintains saidthyristor in substantially nonconductive state when said applied signalis within said predetermined amplitude range and places said thyristorin conductive state when said applied signal is within a secondamplitude range, and wherein the amplitude of said triggering pulse iswithin said second amplitude range whereby said thyristor is placed inthe conductive state when said influencing means is not in said vicinityand is maintained in the nonconductive state when said influencing meansis within said vicinity.

3. A circuit as in claim 2 wherein said electromagnetic circuit meanscomprises a coil and said influencing means comprises means foraffecting the magnetic field of said coil.

4. A circuit for indicating the position within a given vicinity of anobject having electromagnetic field'influencing properties, said circuitcomprising a thyristor controlled output circuit including a thyristorhaving a gate electrode and two other electrodes having conductiontherebetween when said thyristor is in the conductive state, an outputload and alternating power supply input means connected between said twoother electrodes; pulse circuit means connected to and synchronized bysaid alternating power source input means for providing a triggeringpulse at a predetermined time after the beginning of each alternation ofsaid alternating power source, control means coupled to said gateelectrode of said thyristor for controlling the operation thereof inresponse to applied pulses in a predetermined amplitude range; andtranslating said applied signal is within said predetermined amplituderange and places said thyristor in the conductive state when saidapplied signal is within a second amplitude range, and wherein theamplitude of said triggering pulse is within said second amplitude rangewhereby said thyristor is placed in the conductive state when saidinfluencing means is not in said vicinity and is maintained in thenonconductive state when said influencing means is within said vicinity.

6. A circuit as in claim 5 wherein said electromagnetic circuit meansincludes a coil. I

7. A circuit as in claim 5 wherein said electromagnetic circuit meansincludes a transformer.

8. A circuit as in claim 5 wherein said control means comprises atrigger circuit having a voltage breakdown triggering element.

9. A circuit as in claim 5 wherein said control means includes triggercircuit means comprising transistors.

10. A circuit as in claim 4 wherein said pulse circuit means includes afirst RC charging circuit coupled across said alternating power supplyinput means and a trigger circuit connected to said first RC chargingcircuit whereby said pulse circuit means provides a trigger pulse at apredetermined time after the beginning of each alternation of saidalternating power supply.

11. A circuit as in claim 10 wherein said trigger circuit comprises atransistor switching circuit.

12. A circuit as in claim 10 wherein said trigger circuit comprises afirst voltage breakdown triggering element and wherein said controlcircuit comprises a second voltage breakdown triggering element having abreakdown voltage smaller than said first voltage breakdown element.

13. A circuit as in claim 10 wherein said trigger circuit comprises afirst voltage breakdown triggering element and wherein said controlcircuit comprises a second voltage breakdown triggering element havingsubstantially the same breakdown voltage as said first voltage breakdownelement and wherein a second RC charging circuit is provided betweensaid first RC charging circuit and said control circuit and in additivecombination with the output of said translating circuit applied to saidcontrol means.

1. A circuit for the touchless control of a thyristor in response to the approachment in the vicinity of said circuit of a predetermined electromagnetic field influencing means, said circuit comprising a thyristor controlled output circuit including a thyristor having a gate electrode and two other electrodes having conduction therebetween when said thyristor is in the conductive state, alternating power source input means connected across said two other electrodes, pulse circuit means connected to and synchronized by said alternating power source input means for providing a triggering pulse at a predetermined time after the beginning of each alternation of said alternating power source, control means coupled to said gate electrode of said thyristor for controlling the operation thereof in response to an applied pulse in a predetermined amplitude range, and translating means coupled to said pulse circuit means for applying said triggering pulse to said control means, said translating means including touchless electromagnetic circuit means operable in response to the approachment of said influencing means to establish said input pulse in said predetermined amplitude range.
 2. A circuit as in claim 1 wherein said control means maintains said thyristor in substantially nonconductive state when said applied signal is within said predetermined amplitude range and places said thyristor in conductive state when said applied signal is within a second amplitude range, and wherein the amplitude of said triggering pulse is within said second amplitude range whereby said thyristor is placed in the conductive state when said influencing means is not in said vicinity and is maintained in the nonconductive state when said influencing means is within said vicinity.
 3. A circuit as in claim 2 wherein said electromagnetic circuit means comprises a coil and said influencing means comprises means for affecting the magnetic field of said coil.
 4. A circuit for indicating the position within a given vicinity of an object having electromagnetic field influencing properties, said circuit comprising a thyristor controlled output circuit including a thyristor having a gate electrode and two other electrodes having conduction therebetween when said thyristor is in the conductive state, an output load and alternating power supply input means connected between said two other electrodes; pulse circuit means connected to and synchronized by said alternating power source input means for providing a triggering pulse at a predetermined time after the beginning of each alternation of said alternating power source, control means coupled to said gate electrode of said thyristor for controlling the operation thereof in response to applied pulses in a predetermined amplitude range; and translating means coupled to said pulse circuit Means for applying said triggering pulse to said control means, said translating means including electromagnetic circuit means operable in response to the approachment of said object to establish said input pulses in said predetermined range whereby the average power presented to the output load current of said output circuit indicates the presence and absence of said object within said vicinity.
 5. A circuit as in claim 4 wherein said control means maintains said thyristor in substantially nonconductive state when said applied signal is within said predetermined amplitude range and places said thyristor in the conductive state when said applied signal is within a second amplitude range, and wherein the amplitude of said triggering pulse is within said second amplitude range whereby said thyristor is placed in the conductive state when said influencing means is not in said vicinity and is maintained in the nonconductive state when said influencing means is within said vicinity.
 6. A circuit as in claim 5 wherein said electromagnetic circuit means includes a coil.
 7. A circuit as in claim 5 wherein said electromagnetic circuit means includes a transformer.
 8. A circuit as in claim 5 wherein said control means comprises a trigger circuit having a voltage breakdown triggering element.
 9. A circuit as in claim 5 wherein said control means includes trigger circuit means comprising transistors.
 10. A circuit as in claim 4 wherein said pulse circuit means includes a first RC charging circuit coupled across said alternating power supply input means and a trigger circuit connected to said first RC charging circuit whereby said pulse circuit means provides a trigger pulse at a predetermined time after the beginning of each alternation of said alternating power supply.
 11. A circuit as in claim 10 wherein said trigger circuit comprises a transistor switching circuit.
 12. A circuit as in claim 10 wherein said trigger circuit comprises a first voltage breakdown triggering element and wherein said control circuit comprises a second voltage breakdown triggering element having a breakdown voltage smaller than said first voltage breakdown element.
 13. A circuit as in claim 10 wherein said trigger circuit comprises a first voltage breakdown triggering element and wherein said control circuit comprises a second voltage breakdown triggering element having substantially the same breakdown voltage as said first voltage breakdown element and wherein a second RC charging circuit is provided between said first RC charging circuit and said control circuit and in additive combination with the output of said translating circuit applied to said control means. 